Reading Shipbuilding Drawings, Weld Symbols, and Work Orders — Shipbuilding / Marine Fabrication

Objective. Students extract dimensions, weld type, groove geometry, and material specification from a set of multi-view orthographic shipbuilding drawings and annotate a blank reference line with the correct AWS A2.4 weld symbol for a specified joint, achieving at least 80% on a drawing-reading exercise.

Why Drawing Literacy Matters in the Shipyard

Every piece of steel that goes into a vessel begins as a line on a drawing. Shipfitters, welders, and marine fabricators who cannot read those lines accurately produce parts that do not fit, welds that fail inspection, and rework that costs time and money. This lesson teaches you to extract reliable information from shipbuilding structural drawings, decode AWS A2.4 weld symbols, and act correctly on a written work order.

Multi-View Orthographic Drawings

Shipbuilding drawings use standard orthographic projection: the part is shown from the front (body plan), side (profile), and top (half-breadth plan). Each view shares dimensions with its neighbors, so a width shown in the front view matches the width shown in the top view. When you pick up a structural drawing, orient yourself first:

1. Find the title block. It lists the vessel name or hull number, drawing number, revision letter, scale, material specification, and the approval signatures. Never begin work from a drawing that lacks an approved signature or that has been superseded by a later revision.

2. Read the bill of materials (BOM). The BOM is a table, usually in the upper-right corner, that lists every part number, its description, the material specification (for example, ASTM A131 Grade A mild shipbuilding steel), quantity, and sometimes the unit weight. Match each part number to its balloon callout on the drawing before you measure anything.

3. Check the scale and the notes block. General notes override individual callouts only where stated. Tolerances, surface preparation requirements, and weld procedure references often live in the notes block.

4. Measure from datelines, not from the edge of the paper. Ship structure is dimensioned from the vessel's centerline, the baseline (bottom of keel), and frame stations. Know which reference plane each dimension originates from.

Reading a Transverse Web Frame Drawing

A transverse web frame is a vertical ring of plate and stiffeners that runs across the beam of the ship at a specific frame station. The drawing will show the web plate, face flat (flange), bracket connections at the shell and tank top, and all cutouts for pipe penetrations and lightening holes. Typical items to record on your answer sheet include:

Part number and description for every component
Plate thickness for the web and face flat
Height and width of the frame
Dimensions and edge distances for every bracket
Diameter and location of every cutout
The weld symbol at each joint

If a dimension is marked with a revision cloud—a freehand cloudy outline around the change—that dimension has been altered since the previous revision. Always note the current revision letter and compare it to the revision block to confirm you are working from the latest issue.

AWS A2.4 Weld Symbols

AWS A2.4 is the American Welding Society standard that defines a universal shorthand for weld requirements. Every weld symbol is built on a reference line drawn horizontally, with an arrow pointing to the joint. Information placed below the reference line applies to the arrow side of the joint; information placed above applies to the other side.

Key elements of a complete weld symbol:

Weld symbol (geometry): the small shape on the reference line that indicates the weld type—fillet (triangle), groove (V, bevel, J, U, square, flare), plug, slot, or surfacing.
Size: a number to the left of the weld symbol, indicating leg size for a fillet or groove depth for a groove weld.
Length and pitch: numbers to the right of the symbol, written as length–pitch for intermittent welds.
Groove angle and root opening: shown inside or below the groove symbol.
Contour and finish symbols: a straight line (flush), convex arc, or concave arc above or below the weld symbol; a letter indicates the finishing method (G = grind, C = chip, M = machine).
Tail: a forked split at the end of the reference line opposite the arrow; it references the weld procedure specification (WPS) or special instruction.
All-around symbol: a small circle at the arrow-reference-line junction means the weld goes completely around the joint.
Field weld flag: a filled flag at the junction means the weld is made in the field (on the vessel), not in the shop.
Backing bar: a rectangle below the groove symbol; an "R" inside it means the backing is removable.

When you decode a symbol, work systematically: identify the weld type, then read size, then length/pitch, then contour, then any tail reference.

Work Orders and Revision Clouds

A work order is the official authorization to perform a specific task. In a shipyard, it typically includes the drawing number and revision, a plain-language description of the work, material callouts, the applicable weld procedure specification (WPS), and any hold points—stages where an inspector must examine and sign off the work before it continues. You may not weld over a hold point without written inspector approval.

When a drawing carries a revision cloud, your first task is to find what changed. Compare the current revision letter in the title block to the revision history block; the description of the change is listed there. Record the old value, the new value, and the affected part or dimension. Proceeding with an outdated dimension is a recordable quality nonconformance and can require cutting out completed welds.

Safety Considerations

Drawing review is a low-hazard activity, but the decisions made during it drive real hazards later. Before you begin any fitting or welding task:

Confirm the drawing is the current approved revision—working from a superseded drawing is a quality and safety risk.
Verify that the material specification on the drawing matches the material in hand; different alloys require different WPS documents and preheat requirements.
Note any confined-space or hot-work permit requirements called out in the work order notes.
If the work order references a hold point, treat it as a hard stop—never weld past a hold point without documented inspector release.

Key terms8

Orthographic projectionA drafting method that shows an object in two or more flat views (front, top, side), each view at 90 degrees to the others, so that true dimensions can be measured directly from the drawing.

Bill of materials (BOM)A table on a shipbuilding drawing that lists every part by number, description, material specification, and quantity required for the assembly.

Reference lineThe horizontal line that is the foundation of every AWS A2.4 weld symbol; all other symbol elements are placed above, below, or at the ends of this line.

Arrow side / other sideThe two sides of a weld joint as defined by the arrow on the weld symbol; symbol information below the reference line applies to the arrow side, and information above applies to the other (far) side.

Revision cloudA freehand looping outline drawn on a revised drawing to highlight exactly what changed from the previous revision; always check the revision block to confirm the current letter and read the change description.

Hold pointA mandatory inspection stop written into a work order or quality plan; work cannot proceed past this stage until an authorized inspector has examined and approved the work in writing.

Weld Procedure Specification (WPS)A written document that prescribes the welding process, base metal, filler metal, preheat, interpass temperature, and other essential variables required to produce a sound weld meeting the applicable code.

AWS A2.4The American Welding Society standard that establishes the symbols used on drawings to communicate all requirements for a weld—type, size, length, contour, finish, and process—without written notes.

In class: Drawing interpretation session: each student receives a reduced-size structural drawing of a ship's transverse web frame; working individually, students list all part numbers, bill-of-materials items, and critical dimensions on a structured answer sheet, then compare against an answer key in a class debrief. · Weld symbol decode-and-build: instructor presents 15 weld symbols drawn to AWS A2.4 conventions; students write out in plain language what each symbol requires (process, position, size, finish, backing), then sketch the corresponding joint cross-section. · Work-order reading exercise: students receive a realistic typed work order for fitting and welding a bilge-keel bracket, including a revision cloud on the drawing; they must identify which dimension changed, what material was substituted, and what inspection hold point applies before welding.
Materials: Set of shipbuilding structural drawings (industry-sourced or instructor-prepared to realistic standards); AWS A2.4 Standard Symbols for Welding, Brazing, and Nondestructive Examination (current edition, reference copy); AWS A3.0 welding terminology reference; sample work orders and revision-cloud drawing; drafting templates.
Check: Drawing-reading exercise graded against answer key: 80% correct on dimensions and specifications extracted. Weld symbol decode scored: 12 of 15 correct (80%). Work-order exercise: student must correctly identify the revision, material change, and hold point—all three required for pass.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.